Atomizing pumps which dispense a quantity of liquid in a fine spray are generally constructed with a metallic coil spring which is used to bias the pump piston axially outwardly. More often than not, the spring is located within the pump chamber, or below the pump chamber in a location through which liquid flows on its way to the pump chamber. Examples of pumps which include a metallic coil spring in the pump chamber include U.S. Pat. Nos. 3,211,346; 3,746,260 and 4,113,145. Examples of pumps which include a metallic coil spring in a location through which liquid flows on its way to the pump chamber include U.S. Pat. Nos. 4,025,046; 4,122,982 and 4,389,003. In all of these pumps, the liquid to be dispensed contacts the metallic spring as it passes from the container to the atmosphere via the pump.
Although many atomizing pumps are still manufactured with metallic valve mechanisms, other pumps have been created which eliminate the need for metallic valve mechanisms. An example of the latter is shown in U.S. Pat. Nos. 4,113,145; 4,144,987 and 4,389,003. However, these pumps still include a metallic coil spring which is in contact with the liquid to be dispensed. The contact of liquids with metallic elements, either valves or springs, can result in unwanted chemical reactions which can degrade either the liquid or the metallic elements. Furthermore, the existence of metallic parts within a plastic pump makes the pump difficult to recycle, as the metallic parts must be removed from the plastic before it is remelted.
Another form of atomizing pump which has come into use in recent years is the so-called "precompression" pump. This type of pump has an outlet valve which opens in response to a predetermined minimum pressure in the chamber. This is generally accomplished by including a valve member or stem within the pump chamber which has a net upwardly-facing surface upon which pressure acts. When the pressure acting on this valve member is sufficiently high, it overcomes a biasing spring, pushing the valve member downwardly and opening the outlet valve. Examples of these types of pumps are found in U.S. Pat. Nos. 3,399,836; 4,025,046; 4,144,987 and 4,389,003. These pumps use a single metallic coil spring, which urges the valve member as well as the piston member upwardly. Because this one spring is used to resist pressure action on the valve stem and to return the pump piston, the spring must be sufficiently stiff to provide both functions. However, this high stiffness requires an operator to press down with a fairly high actuation force on the actuator to ensure spraying. High actuation force is sometimes difficult to achieve for the elderly, children and some women; the result is that these precompression pumps are sometimes perceived as difficult to operate by certain people.